Influence of interleukin-4 gene polymorphisms and interleukin-4 serum level on susceptibility and severity of rheumatoid arthritis in Egyptian population
Highlights
► IL-4-590 TT genotype and T allele frequencies were significantly increased in RA. ► IL-4 VNTR and IL-4-590 polymorphisms were significantly associated with erosive RA. ► IL-4 VNTR and -590 polymorphisms were significantly associated with anti-CCP+ RA. ► RA patients with IL-4 VNTR 1/1 and IL-4-590 TT genotypes had lower IL-4 levels. ► RA patient with IL-4-590 TT genotype showed significant increase of RA activity.
Introduction
Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease affecting approximately 1% of the world’s population, with higher prevalence in women than in men (3:1 ratio). Both environmental and genetic factors contribute to the etiology, pathogenesis and/or clinical severity of this disease [1].
Research shows that the imbalance of T helper 1 (Th1)/T helper 2 (Th2) cells ratio results in the development and progression of RA [2]. Th1 cells secrete interferon-γ (IFN-γ) and interleukin-2 (IL-2) mediating pro-inflammatory functions by activating antigen presenting cells and T cell proliferation respectively. IL-4, IL-5 and IL-10, secreted by Th2 cells, suppress cell-mediated immunity by counteracting Th1 response and promote humoral immunity by enhancing B cell response [3], [4]. Therefore, polymorphisms affecting genes of these cytokines can be linked with RA risk and become of great interest to researchers [5].
IL-4, a potent anti-inflammatory cytokine, is produced by activated CD4+ lymphocytes, mast cells and basophils. It exerts immune modulatory functions on different cell types [6], increases immunoglobulin E (IgE) production and serves as an important regulator of IgG isotype switching [7]. Furthermore, it inhibits the production of destructive protease enzymes and pro-inflammatory cytokines, such as IL-1, by increasing the expression of interleukin-1 receptor antagonist (IL-1RA) [8], [9]. It is a key factor in the polarization of T helper cells toward Th2 differentiation, which are deficient in rheumatoid synovial tissues [10]. Several studies suggest that IL-4 and its receptor may control the inflammation induced by Th17, a third CD4+ T-cell population, which plays a central role in the pathogenesis of human autoimmune diseases, including RA [11]. Moreover, in a mouse model of collagen-induced arthritis, monoclonal antibodies against IL-4 lead to greater severity of the disease, supporting the protective role of IL-4 in RA [12].
IL-4 gene has been mapped to the q arm (q23–31) of chromosome 5 [13]. IL-4-590 promoter polymorphism, representing a C-to-T base substitution at 589 base pair (bp) upstream of the transcriptional site, has been recently identified [14]. Several studies suggested its association with early pauciarticular juvenile rheumatoid arthritis [15]. A variable number of tandem repeat (VNTR) polymorphism is another polymorphism that is located in the third intron of IL-4 gene. Its frequent allelic form consists of three 70 base pair (bp) repeats in intron 3 [16]. Previous studies examined the association of IL-4 gene polymorphisms with RA [13], [17]. However, their data are conflicting; therefore, further studies in different populations are essentials.
Anti-cyclic citrullinated peptides (anti-CCPs) antibody is an important diagnostic and prognostic marker of RA, being present early in the course of the disease and slightly affected by the treatment [18], [19]. It was included in the new criteria for diagnosing RA by the American College of Rheumatology and the European League Against Rheumatism 2010 (2010 ACR–EULAR classification criteria) [20], [21]. The tight control of RA activity improves the disease outcome, so, early identification of patients is essential to enhance their care [22]. On the basis of these considerations, we designed this study to investigate the association of IL-4 VNTR and IL-4-590 promoter polymorphisms with RA susceptibility, activity and severity in Egyptian population.
Section snippets
Materials and methods
One hundred and seventy-two unrelated patients with RA (mean age 47.39 ± 9.3 years), diagnosed according to 2010 ACR–EULAR classification criteria for rheumatoid arthritis, were recruited from the follow-up and inpatient units of Rheumatology and Rehabilitation department, Zagazig University hospitals, Egypt [21]. Characteristics of RA patients were summarized in (Table 1). The control group included 172 healthy subjects (mean age 49.35 ± 8.7 years) with no family history of any autoimmune diseases.
Association of IL-4 VNTR and IL-4-590 promoter polymorphisms with RA susceptibility
The genotype frequencies of IL-4 VNTR and IL-4-590 promoter polymorphisms were all in accordance with the Hardy–Weinberg equilibrium in all groups. In RA patients, the frequencies of IL-4-590 TT genotype and T allele were significantly increased compared to the control group. Subjects with IL-4-590 TT genotype and carriers of T allele were significantly more likely to develop RA (OR = 8.54, 95% CI = 2.47–29.59, P = 0.003) and (OR = 2.17, 95% CI = 1.49–3.17, P = 0.025) respectively. On the contrary, the
Discussion
Rheumatoid arthritis is an autoimmune disease which primarily attacks the joints resulting in a high rate of deformity [27]. The etiology of RA is still unidentified and may be multifactorial [28]. A combination of various genetic markers may represent a powerful tool in predicting diagnosis and/or prognosis of this disease [29]. O’Dell [30] reported that early treatment may retard disability as joint erosion, so, it is very important to identify reliable markers of RA susceptibility, activity
Conclusion
Our findings provided the evidence that both IL-4 VNTR and IL-4-590 promoter polymorphisms may be helpful for the detection of erosive RA but only IL-4-590 promoter polymorphism was associated with RA susceptibility and activity in Egyptian patients. It remains important to identify other immunological and biochemical markers of RA which can be targeted therapeutically.
Funding
This work was funded by support of academic research in Zagazig University Projects, Zagazig University Postgraduate & Research Affairs.
Competing interests
None declared.
Ethical approval
The study protocol was approved by the ethical committee of Faculty of Medicine, Zagazig University.
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